N.Y. Comp. Codes R. & Regs. tit. 12, § 8-1.54 – Standard railing.

(a) A standard railing shall be of wood or metal not less than three feet six inches high, with an additional rail approximately midway between the top rail and floor level.
(b) Metal railings shall be constructed of not less than one and one-quarter inch standard pipe, or angle iron not less than one and one-half inches by one and one-half inches by three-sixteenths inch, supported on uprights of at least equal dimensions, spaced not more than eight feet center to center.
(c) Wooden railings shall be of sound lumber, dressed on four sides and constructed as follows:
1. (1) Top railing shall be not less than two inches by four inches, or one inch by four inches, provided another board of not less than one inch by four inches is securely nailed to sides of posts and to top rail.
2. (2) Center railing shall be not less than one inch by four inches, supported on not less than two inch by four inch posts, spaced not more than eight feet center to center.
  Note:
  It is recommended that four-inch by four-inch posts be used. Dimensions given above are rough lumber sizes; dressed lumber will be one-eighth inch to three-eighths inch smaller, and will be accepted.